Write Ahead Log
Write Ahead Log (WAL) is a database and system design concept where all modifications to data are first recorded in a persistent log before being applied to the main data structures. This ensures durability and atomicity by allowing recovery from crashes or failures by replaying the log. It is a fundamental technique in database management systems, file systems, and distributed systems to maintain data integrity and consistency.
Developers should learn and use WAL when building or working with systems that require high reliability, crash recovery, and ACID compliance, such as relational databases (e.g., PostgreSQL, SQLite), distributed databases (e.g., Apache Cassandra), and file systems (e.g., ext4). It is essential for ensuring that transactions are not lost during failures and for enabling features like point-in-time recovery and replication.